1. Field of the Invention
The present invention relates to a contact-type displacement measuring apparatus.
2. Description of the Related Art
Conventionally, a contact-type displacement measuring apparatus is known (for example, “Development of a Nondestructive Surface Geometry Nano-Measuring Apparatus” by Kunitoshi Nishimura, et al., [online], New Energy and Industrial Technology Development Organization, [Retrieved on Jan. 30, 2004], the Internet <URL: http://www.nedo.go.jp/itd/teian/annmtg/fyll/seika/98y28001/98y28001s.html>) that is configured to have a measuring force detecting unit at the tip of a spindle, that detects contact with an object to be measured; a position detecting unit at the center of the spindle, that detects a displacement of the spindle; and a linear actuator at the rear end of the spindle, that moves the spindle in the direction of a shaft line. In a contact-type displacement measuring apparatus having such configuration, measurement of the object is executed by the position detecting unit through the measuring force detecting unit.
FIG. 13 is a schematic diagram of a configuration of a contact-type displacement measuring apparatus disclosed in the above non-patent document “Development of a Nondestructive Surface Geometry Nano-Measuring Apparatus”. As shown in FIG. 13, a spindle 101 that moves vertically is provided in substantially the center of a frame 100. At the tip of the spindle 101, an electric-capacitance-type displacement detector 103 and a stylus 104 are mounted through a piezoelectric element 102 that generates a micro displacement. The stylus 104 is constituted of an oscillator that resonates in the primary mode with a support point as a node of vibration and both ends as antinodes. When the tip of a horn of the oscillator in a resonant state is caused to contact an object 150 to be measured and the oscillator is constrained, the resonant state of the stylus 104 changes.
The change of the resonant state is detected by a detecting electrode. Thereby, it is detected that the tip of the stylus 104 has contacted the object 150 to be measured. At the rear end of the spindle 101, a moving-coil-type actuator 105 that generates a rough displacement is disposed. According to a fine-and-rough driving scheme by this moving-coil-type actuator 105 and the piezoelectric element 102, micro displacements are measured by the piezoelectric element 102 and large displacements are measured by the moving-coil-type actuator 105 when the tip of the stylus 104 is caused to follow the shape of the object to be measured.
As an amount to be measured in a direction of Z-axis (direction perpendicular to the plane that the tip of the stylus 104 contacts) of the shape of the object, a value detected by the electric-capacitance-type displacement detector 103 is used. A surface geometry measuring apparatus is known (for example, Japanese Patent Application Laid-Open Publication No. H6-147886) that is configured to have parallel springs on a bottom face of a movable body capable of micro moves; and, on one end of the parallel springs, a contact finger that contacts a surface to be measured; a movable body displacement detecting unit that detects the amount of a displacement of the movable body; and an resilient body displacement detecting unit that detects the amount of a displacement of the parallel springs.
However, in the contact-type displacement measuring apparatus disclosed in the above non-patent document, when the tip of the stylus contacts the object to be measured and the oscillation mode of the oscillator changes, distortion is generated in the measuring force detecting unit and the dimensions of the measuring force detecting unit itself change. Therefore, an error is generated when the object is measured and such a problem arises that correct measurement results and reproducible measurement results can not be obtained. Because the portion that contact the object is constituted of a stylus, another problem arises that measurement can not be executed using a probe, mounted on the tip of the spindle, that is used in a common contact-type displacement measuring apparatus and that fits the shape of the object.
In the surface geometry measuring apparatus disclosed in Japanese Patent Application Laid-Open Publication No. H6-147886, when the contact finger moves upward and downward following the surface geometry of the surface to be measured, the parallel springs are deformed in response to the movement. Therefore, the lateral position of the contact finger mounted on the tip of the parallel springs is shifted to the base end side of the parallel springs. Therefore, such a problem arises that an error is generated in the measurement result.